The present invention relates to a method and apparatus for comminution of fibrous materials, such as tobacco, and more particularly to improvements in a method and apparatus for shredding tobacco leaves or fragments of tobacco leaves.
A tobacco shredding apparatus normally comprises a rotary carrier for one or more knives which remove shreds from the leader of a continuous cake of compacted tobacco. The cake is formed and its contents compacted by a feeding device which preferably includes two chain conveyors or other types of conveyors defining a gradually narrowing path extending from a source (e.g., the lower end of a tobacco duct) to a comminuting station where the leader of the cake moves into the range of orbiting knives. As a rule, the knife carrier is driven by a first motor and the chain conveyors of the feeding device are driven by a second motor which can be started or arrested independently of the first motor. The knife or knives on the carrier are sharpened by a grinding wheel which is dressed by a diamond or the like and preferably (but not necessarily) receives torque from a separator motor.
Shredding apparatus of the just outlined character are often set up in groups of two, three or more, i.e., an entire battery of shredding apparatus can be employed to comminute large quantities of tobacco ahead of a conditioning unit which changes the moisture content and/or temperature of shreds and/or contacts the shreds with casing or other flavoring agents prior to introduction of shreds into the distributor of a machine for the production of plain cigarettes, cigarillos or cigars. Even minor defects of a shredding apparatus or of means for supplying tobacco to or for removing tobacco shreds from such apparatus normally necessitate an interruption of the feed of tobacco cake into the range of orbiting knives in the respective apparatus. Furthermore, the feed of tobacco cake to a shredding apparatus must be interrupted if the feeding means is to receive a different blend of two or more tobacco types. A short interruption of the feed does not necessarily (and normally does not) entail a stoppage of the knife carrier. Therefore, and since the leader of the compacted cake (whose forward progress has been interrupted in order to eliminate a defect or for other purposes) exhibits a strong tendency to expand, the front surface of the expanding leader moves into the range of the orbiting knives which remove (actually scrape) minute fragments of tobacco from the cake. The fragments are much smaller than normal tobacco shreds. Moreover, the expanding leader of an arrested tobacco cake moves into strong frictional engagement with the rapidly orbiting knives and/or with the rotating carrier whereby the aforementioned minute fragments undergo a pronounced drying and heating action. The heating action is so pronounced that the fragments of tobacco are likely to be combusted, for example, due to generation of sparks which develop on contact between the grinding wheel and the orbiting knives. Therefore, fires in conventional shredding apparatus and/or in filters which are used to intercept tobacco dust that is removed from shredding apparatus and the surrounding area are not uncommon. Such fires can cause extensive damage to tobacco and to equipment in a tobacco processing plant as well as prolonged interruptions of operation which is particularly undesirable when the shredding apparatus are installed in a complete production line.